Finished lubricants used for automobiles, diesel engines, axles, transmissions, and industrial applications consist of two general components, a lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Numerous governing organizations, including original equipment manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d'Automobiles (ACEA), the American Society of Testing and Materials (ASTM), and the Society of Automotive Engineers (SAE), among others, define the specifications for lubricating base oils and finished lubricants. Increasingly, the specifications for finished lubricants are calling for products with excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Lubricating base oils are base oils having a viscosity of about 3 cSt or greater at 100 degrees C., preferably about 4 cSt or greater at 100 degrees C.; a pour point of about 9 degrees C. or less, preferably about −15 degrees C. or less; and a VI (viscosity index) that is usually about 90 or greater, preferably about 100 or greater. In general, lubricating base oils should have a Noack volatility no greater than current conventional Group I or Group II light neutral oils. Group II base oils are defined as having a sulfur content of equal to or less than 300 ppm, saturates equal to 90 percent or greater, and a VI between 80 and 120. A Group II base oil having a VI between about 110 and 120 is referred to in this disclosure as a Group II plus base oil. Group III base oils are defined as having a sulfur content of equal to or less than 300 ppm, saturates equal to 90 percent or greater, and a VI of greater than 120. It would be advantageous to be able to boost the VI of a Group II base oil into the Group II plus and the Group III base oil range. The present invention makes it possible to lower pour point and raise VI. Depending upon the amount of pour point depressing base oil blending component added to the base oil blend, the Noack volatility may also be lowered and the viscosity of the base oil may be raised.
Base oil refers to a hydrocarbon product having the above properties prior to the addition of additives. That is, the term “base oil” generally refers to a petroleum or syncrude fraction recovered from the fractionation operation. “Additives” are chemicals which are added to improve certain properties in the finished lubricant so that it meets relevant specifications. Conventional pour point additives are expensive and add to the cost of the finished lubricant. Some additives also present solubility problems and require their use along with a solvent. Consequently, it is desirable to use the minimum amount of an additive necessary to produce an on specification lubricant.
Pour point which is an important property of base oils intended for blending into finished lubricants is the lowest temperature at which movement of the base oil is observed. In order to meet the relevant pour point specification for a finished lubricant, it is often necessary to lower the pour point of the base oil by the addition of an additive. Conventional additives which have been used to lower the pour point of base oils are referred to as pour point depressants (PPDs) and typically are polymers with pendant hydrocarbon chains that interact with the paraffins in the base by inhibiting the formation of large wax crystal lattices. Examples of pour point depressants known to the art include ethylene-vinyl-acetate copolymers, vinyl-acetate olefin copolymers, alkyl-esters of styrene-maleic-anhydride copolymers, alkyl-esters of unsaturated-carboxylic acids, polyalkylacrylates, polyalklymethacrylates, alkyl phenols, and alpha-olefin copolymers. Many of the known pour point depressants are solid at ambient temperature and must be diluted drastically with solvent prior to use. See Factors Affecting Performance of Crude Oil Wax-Control Additives by J. S. Manka and K. L. Ziegler, World Oil, June 2001, pages 75–81. Pour point depressants taught in the literature have a wax-like paraffinic part, which co-crystallizes with the wax-forming components in the oil, and a polar part which hinders crystal growth. The pour point depressing base oil blending component employed in the present invention differs from pour point depressants known from the prior art in being essentially both aromatic-free and polar-free. One of the advantages of the present invention is that the pour point depressing base oil blending component of the present invention is not an additive in the conventional sense. The pour point depressing base oil blending component used in the invention is only a high boiling syncrude fraction which has been isomerized under controlled conditions to give a specified degree of alkyl branching in the molecule. Therefore, it does not lend itself to problems which have been associated with the use of conventional additives.
Syncrude prepared from the Fischer-Tropsch process comprises a mixture of various solid, liquid, and gaseous hydrocarbons. Those Fischer-Tropsch products which boil within the range of lubricating base oil contain a high proportion of wax which makes them ideal candidates for processing into lubricating base oil stocks. Accordingly, the hydrocarbon products recovered from the Fischer-Tropsch process have been proposed as feedstocks for preparing high quality lubricating base oils. When the Fischer-Tropsch waxes are converted into Fischer-Tropsch base oils by various processes, such as by hydroprocessing and distillation, the base oils produced fall into different narrow-cut viscosity ranges. Those Fischer-Tropsch cuts which have properties which make them suitable for preparing lubricating base oils are particularly advantageous for blending with marginal quality conventional base oils or Fischer-Tropsch derived base oils due to their low volatility, low sulfur content, and excellent cold flow properties. The bottoms that remains after recovering the lubricating base oil cuts from the vacuum column is generally unsuitable for use as a lubricating base oil itself and is usually recycled to a hydrocracking unit for conversion to lower molecular weight products. Applicant has found that the high molecular weight hydrocarbons associated with the bottoms when properly processed are particularly useful for improving the lubricating properties of base oils, either conventionally derived or Fischer-Tropsch derived.
As used in this disclosure the phrase “Fischer-Tropsch derived” refers to a hydrocarbon stream in which a substantial portion, except for added hydrogen, is derived from a Fischer-Tropsch process regardless of subsequent processing steps. Accordingly, a “Fischer-Tropsch derived bottoms” refers to a hydrocarbon product recovered from the bottom of a fractionation column, usually a vacuum column, which was initially derived from the Fischer-Tropsch process. When referring to conventional base oils, this disclosure is referring to conventional petroleum derived lubricating base oils produced using petroleum refining processes well documented in the literature and known to those skilled in the art. The term “distillate base oil” refers to either a “Fischer-Tropsch derived” or “conventional” base oil recovered as a side stream from a fractionation column as opposed to the “bottoms”.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” are intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.